Reinforced abrasive products



March 11,A 1958 E. HURST y 2,826,016

REIFORCED ABRASIVE PRODUCTS Filed Feb. 6, 1956 ETE F J.Ea.

IN V EN TOR.

ATTORNEY i EDWARD HURS7 nite States Patent() REINFORCED ABRASIVE PRODUCTS Edward Hurst, Duxbury, Mass., assignor to Rexall Drug Co., Los Angeles, Calif., a corporation of Delaware Application February 6, 1956, Serial No. 563,731

14 Claims. (Cl. 51-206) This invention relates to the manufacture of abrasive articles of the bonded type such as grinding wheels; more particularly, it relates to abrasive articles of the described type which, regardless of size or shape, require the presence of reinforcing elements to strengthen them against breakage during use. The invention specifically pertains to improvements in the means for reinforcing such abrasive articles and the improved abrasive products resulting therefrom.

The problem of breakage in the grinding wheel industry has been long standing and serious. Anyone who has had the unpleasant experience of being present at the unexpected breakage and disruption of an abrasive wheel during its use is vividly aware of the great risk of damage and personal risk which can result from such happenings. The final answer to this problem obviously cannot be the further strengthening of the bonding materialholding the abrasive grains together since it is essential to the satisfactory performance of an abrasive wheel of the bonded type that the bond gradually break down during use and impart to the abrasive Wheel the necessary free cutting action for efficient operation. The problem has been partially met in some abrasive articles, especially those for heavy duty usage, by the provision of some form of reinforcing element within or external to the article.

For example, limited strengthening of bonded abrasive wheels has been obtained in some instances by the incorporation in the wheel of a multitude of randomly disposed short lengths of chopped fiber or wire. Grinding wheels have also been heretofore reinforced by the incorporation within the wheel of cotton fabrics and similar textile fabric sheet materials of relatively low strength in the hope that the materials used as reinforcements will break down sufficiently at the grinding surface of the wheel so as not to interfere with the grinding action. Stronger reinforcements such as steel bars and rods have been embedded within the body ofthe grinding article at points remote from the grinding surface of the article in order to provide greater overall strength to the product although this has been at a sacrifice of the usefulness of that part of the abrasive body containing the reinforcing element or elements. Side flanges, wire Wrappings and other external members extending almost to the wheel periphery or grinding face have been designed to lessen the dangers from wheel breakage as much as possible with- 4out interfering with the usefulness of the wheel. None Iof these prior efforts have fully solved the problem of wheel breakage in the grinding wheel industry and the `demand remains for abrasive products of the grinding wheel type which will not only be adequately strengthened against breakage during use but will also give satisfactmy grinding performance and be useful throughout. i

It is an object of the present invention therefore to more fully meet this need and provide reinforced abrasive products of the grinding wheel type which will be adequately reinforced for their intended usage.

r It is a second object to provide reinforced yabrasive will be described in further detail later herein.

y tion to the periphery in all directions, or disposeed heli#l I i tended use.

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products of the grinding Wheel type which will be adequately reinforced for their intended usage and in which the presence of the reinforcements not only do not interfere with the grinding action of the product, but in fact are highly beneficial in improving the grinding action of the product. In other words, it is the two-fold object of the present invention to provide reinforced abrasive products in which the reinforcements perform the dual function of strengthening the product and improving its grinding efficiency.

According to the present invention an abrasive article of the grinding wheel type is provided with one or more reinforcing elements which are of sufiicient tensile strength to overcome any disruptive forces if the .abrasive body of the article should fail and thus prevent the grinding wheel or other abrasive article from flying apart, and effectively strengthen the abrasive body against breakage at substantially all points. Furthermore, the reinforcing element orelements so provided actually improves the normal cutting performance of the abrasive body. i accomplish this by embodying in the wheel or other shape a compound or composite reinforcement comprising as one essential component long, fibrous or filamentary base material of adequate tensile strength in close association with a second component of ignitable-or pyrophoric characteristics whichwill act upon the high tensile strength fibrous or iilamentary material of thev reinforcement at the grinding surface of the abrasive article and cause the end of the entire reinforcement at the grinding face of the abrasive article to disintegrate. This disintegrating action at the grinding face removes the reinforcing material from the grinding face of the article where it would otherwise interfere with the cutting action of the abrasive body and instead leaves a small recess or clearance space which serves to introduce additional sharp cutting edges within the cutting face and thereby improve the cutting efficiency of the abrasive body. This disintegration of the reinforcing element or elements at the face of the abrasive body does not extend more than 1&2 in from the grinding face of the abrasive body, and usually is no deeper than 10,4. Moreover, the reinforcement within the abrasive body remains otherwise unmpaired and continues to perform its full `strengthening function. d

The reinforcing element or elements can take any desired fabricated form depending upon the specific size and/or shape of abrasive article to be reinforced. For example, in reinforcing grinding wheels of the most common shape having two parallel straight sides and a peripheral grinding or cutting face or edge the reinforcing element can take the form of disc shaped or annular plies of structural material substantially coextensive in area with the diametrical dimensions of the particular abrasive wheel to be reinforced. The structural material constituting the reinforcing element can be woven orv nonwoven or felted construction or composed of a plurality of parallel and/or non-parallel strands deposited or laid down upon a suitable carrier or base material or bonded together without the use of a carrier medium to form an open net-work structural reinforcement such as the special new non-woven filamentary reinforcing structures which Instead of being in the above structural form the reinforcing elements can be in the form of individual separate threads or strands of material disposed, for example, radially in the Wheel body so as to extend from the hub or arbor porcally or spirally within the wheel, or in fact,positioned n the abrasive body in any desired arrangement or configuration, depending upon the specific abrasive body and the way it is to be most desirably reinforced for its in- The fibrous or filamentary'base'material constituting the high tensile strength constituent of the reinforcing element can be any high tensile strength metallic or non-metallic, organic or inorganic, natural or synthetic fibrous or filamentary mateiial of adequate tensile strength to effectively reinforce the abrasive body to the required extent, such as fine steel wire of high tensile strength, nylon yarns or filaments, glass fiber yarn, all of which have been found satisfactory as high tensile strength, fibrous or filamentary materials for the purposes of the present invention.

The second function of the present reinforcing element of improving the grinding etiiciency of the abrasive body by disposing of the reinforcing element at the grinding face of the abrasive body is accomplished by having present a material that will cause burning or disintegration of the strengthening material before it reaches the grinding surface without impairment of the tensile strength of the reinforcement within the body of the article. A very effective means of bringing about this disintegration of the reinforcing element adjacent the grinding surface during the use of the abrasive body is through the use as the second constituent of the reinforcing element thereof of easily oxidizable metal, or other pyrophoric matcrial which will be'ignitcd by the sparks generated in grinding. The burning of the pyrophoric material initiated by the sparks of grinding releases sufficient heat, such as the cxotherrnic heat of reaction, to ignite and burn, fuse, melt, embrittle or otherwise bring the high tensile strength material of the reinforcing element to a disintegrable condition in the immediate vicinity of the grinding surface, that is, to a depth of not more than about l/iig" in from the grinding face, The rest of the reinforcement is unaffected since there is an insufficient supply of oxygen within the abrasive body to support the reaction. Pyrophoric metals such as magnesium, aluminum, silicon and zirconium can be used for this purpose. For example, ne thin aluminum wire can be twisted and/ or entwined about reinforcing filaments of ne steel wire and the composite twisted strand used as a reinforcing material which will provide high strength throughout an abrasive body such as a grinding wheel but which, through spark ignition of the aluminum of the reinforcing element at the g1inding surface of the wheel, will bring about disintegration of the terminal portion of the reinforcing element adjacent the grinding face. Satisfactory results have also been obtained with compound fabric reinforcements composed of glass yarn or nylon fibrous or larnentary fabrics or structures coated with magnesium metal powder adhered to the fibrous or dlamentary material by means of suitable adhesives and incorporated in the abrasive wheels as high strength reinforcing material. which will disintegrate at the grinding face in the course of grinding. Chemical oxidizing agents such as potassium chlorate can be incorporated in the coating along with or as the ignitable or pyrophoric component to promote the effective breakdown of the reinforcement at the grinding face. As further explained elsewhere herein, by the proper embodiment of such cornposits elements within an abrasive body the product is not only strengthened but the grinding performance of the article is enhanced.

in order to better understand the nature of the abrasive articles under consideration, reference is made to the accompanying drawing showing specific examples of abrasive wheels made in accordance with the present invention, and in which:

Figure l is a plan View of a reinforced abrasive cutoff wheel made in accordance with the present invention;

Figure 2 is a sectional View through the line 2 2 of Figure l;

Figure 2a is a highly enlarged fragmentary view of the wheel periphery portion of Figure 2;

Figure 3 is a view similar to Figure 2a showing a grinding wheel of substantial thickness such as the type used in snagging operations, and in which a reinforcing element is embodied in the wheel in accordance with one specific modification of the present invention;

Figure 4 is a plan view of a special construction of reinforcing material which can be used in carrying out the present invention;

Figure 4a is a highly enlarged fragmentary view of one of the individual filaments of filamentary material making up the reinforcing fabric shown in Figure 4; and

Figure 5 is a fragmentary view similar to Figure 2a of an abrasive cutting-off wheel constructed of abrasiveincluded fibrous sheet material and reinforced in accordance with the present invention.

As pointed out briefiy above, the reinforcement employed in carrying out the present invention need not be in any particular structural form. It can be, and usually does comprise, one or more plies or layers of fibrous material, preferably in the form of an open network of spun fibrous yarn or strands of fibrous or filamentary material and in which the reinforcement cousidered as a whole contains strands extending in a plurality of directions in the general plane of the reinforcement to provide high tensile strength in all directions. However, the reinforcement can comprise a plurality of independent strands independently or collectively arranged or disposed within the abrasive body in any desired manner, depending upon the intended usage of the specific abrasive product in which the reinforcement is to be embodied. The selected fabric or yarn or filamentary material is built into the abrasive body to reinforce the latter in accordance with any desired arrangement or disposition of the fabric or yarn although it is preferably so disposed within the body of the abrasive article that the edges of the fabric in the case of sheet material, or the ends of the yarn or filaments in the case of individual strips of yarn or individual filaments, are presented to the grinding surface.

l have designed and developed a new and improved reinforcing material which l have found to be highly satisfactory for use in connection with the present invention, although it is to be understood that the present invention is not in any way limited to the use of this specic structural form of reinforcement. This specific structural reinforcing material or reinforcement, however, is so constructed as to equalize the tensile strength properties of the material so that when it is used as a reinforcement in abrasive Wheels or in other bodies it will impart its reinforcing effect thereto in substantially all directions in the plane of the reinforcement and thereby strengthen the product against stresses regardless of the direction of the forces thereof. Referring to one specific embodiment of this novel reinforcement shown in Figures 4 and 4a, the reinforcement is composed of three separate layers or plies of fibrous strands such as fiber glass yarn or nylon spun yarn or filaments or other filamentary or stranded material of adequate tensile strength in which the individual fiber strands of each ply are laid down in parallelism and laminated with each succeeding layer or'ply of individual strands laid down superimposed upon thc previous layer of fibrous strands Without interweaving of the strands of one layer with other strands of the same layer or with strands of the adjoining layers. The individual yarn or strands 7 of the intermediate layer or laminations and strands 8 of the uppermost layer or lamination are each laid down in parallelism at an angle of 120 from the directional position of the fibrous strands 9 of the bottom-most layer or lamination. The resulting reinforcement consists of a laminated structure in which strands of the structure extend in a plurality of directions. For some purposes of reinforcing where it is undesirable or not necesssary for the reinforcement to break down at the edges, the strands or yarns making up the structure need not be coated, but can be used in uncoated form. However,

when used for reinforcing abrasive articles in accordance with the presently claimed invention, wherein it is desired to promote breakdown of the reinforcement at the grinding face of the article, the filaments or strands are coated with a pyrophoric material. As shown more specifically in Figure 4a, the individual strands 7, 8 and 9 of glass fiber yarn, preferably before being laiddown, are coated with magnesium powder 10, or other pyrophoric material, which is adhered to the fibers of the yarn by means of any suitable adhesive such as starch or aphenolic resin adhesive or the like. The coated strands in forming the individual laminations of the reinforcement are laid down in parallelism in successive layers upon an open network of fine cotton fibers 11 and the entire structure impregnated or treated with a suitable binder to give the material adequate handling strength for integrating into an abrasive body structure. As an alternative to supporting the parallel strands on an open network fabric, the latter can be eliminated entirely and the reinforcement formed by winding the strands of one ply upon a rotating mandrel, and after one Winding is completed, winding again at 120 angle to the first winding of strands, followed by a third winding at a still further angle of 120, the latter windings being superimposed on the first winding to form the structural network of strands making up the reinforcement. Reinforcements of the described lamentary or stranded construction can be formed as continuous structures of any desired width and length and later cut to the size and `shape required for the article being reinforced, or they can be formed as a continuous helical structure such as might be used for reinforcing a grinding Wheel in the manner shown in Figure 3.

It should be pointed out at this time that these novel helical reinforcements are of especial value in reinforcing abrasive bodies and other articles of substantial thickness or volume, or in reinforcing any shape where it 'is desired to incorporate a plurality of layers of reinforcing in the article with the attainment of a maximum of strength. Particularly in the strengthening of abrasive articles of the grinding wheel type these continuous helical reinforcing structures, as will be further brought, forth later herein, offer themselves toa completely new and improved technique for making reinforced abrasive articles. Furthermore, the incorporation of these vhelical reinforcements in abrasive articles in thedescribed manner results in an abrasive article of improved grinding performance. The improved cutting efficiency of such reinforcedarticles is accomplished by the provision inthe grinding surface of a number of sharp cutting edges developed as a result of the facial disintegration of the vreinforcements at the grinding surface. Furthermore, the spiral disposition of such continuous` clearance spaces and cutting edges when located in the wide peripheral cutting edge of an abrasive wheel suchL as asnagging wheel, when the wheel is operated, produces a multiplicity of those cutting edges which as the wheel rotates against the workpiece advances across .the work to give a uniform and much more efficient grinding action than a similar wheel without such disintegrable helical reinforcements. .v While I have referred to these helical reinforcements as being of continuous structure, and I prefer to form them as'such, such helical reinforcements can be fabricated by cutting out a plurality of annular disc shaped pieces of the selected material in the desired diameters, slitting each ofthe annular pieces radially, and splicing the severed annuli to form a continuous helical reinforcement. The splices can be strengthened against breakage by cementing or otherwise securing a strip of suitable fabric across the splice .on one or both sides of the reinforcement.

While I havereferred to these helical reinforcements herein primarily as they have been used in the reinforcing ,of abrasive articles they can be similarly used to reinforce innumerable other articles of manufacture where high strength is a requirement. For example, they can be used rto 'reinforce thespool heads used in .the textile industry.

The exact manner in which" reinforced abrasive articles are constructed in accordance with the present invention Example I Figures l, 2 and 2a show the construction of a 9" X 1" x l" resin-bonded abrasive cutting-off wheel composed of a body 14 of resin bonded abrasive grain, the wheel being reinforced by a single layer of reinforcing material 15 composed of glass yarn strands coated with magnesium metal powder and structurally built up as shown in Figure'4 described hereinabove.

The cutting-off wheel is constructed in accordance with conventional procedure for making reinforced wheels using any suitable composition of abrasive grains of the desired grit size and bonding material in proportion and prepared in accordance with practices well known in the art. The art of making resin-bonded cutting-off wheels, including reinforced cutting-off wheels, is well known in the art and needs no further description here. The present invention is not restricted to any specific abrasive grain or bond composition, but can be practiced with any of the organic resin or rubber bond compositions found satisfactory for bonded abrasive bodies. The selected composition of abrasive grains and bond is introduced into a mold in sufficient amount to form 1/2 of the body or volume of the wheel, a layer of the reinforcing material superimposed upon the abrasive-bond mixture in the mold, after which the remainder of the abrasive-bond mixture is distributed evenly over the surface of the reinforcement. The entire mixture containing the embedded reinforcement is then compacted by pressure and the bond cured at suitable temperature either during the pressing operation or by suitable subsequent oven cure, depending upon the nature of the mix and the facilities available.

Figure 2a shows diagrammatically a peripheral fragment of such an abrasive wheel after it has been used in grinding and shows the manner in which the reinforcement is 4disintegrated during grinding at the peripheral grinding face 16 of the wheel. As a result of the ignition and combustion of the pyrophoric magnesium powder coating with the release of exothermic heat of oxidation the ends of the glass ber strands of the reinforcement are rendered friable and so disintegrate in the immediate vicinity of the grinding surface, leaving a clearance space 17 extending around the grinding periphery of the wheel. As a result of this action the reinforcing layer does not interfere with the normal grinding action of the wheel and, in fact, promotes a greater freedom of cutting action by providing a clearance space for taking away the detritus of grinding as well as the presentation of two additional peripheral cutting edges in addition to those provided by the side edges of the wheel.

Example II Assuming vthat it is the desire to reinforce abrasive wheels of greater body bulk such as a resinoid bonded snagging wheel i6 outside diameter with a 2" wide peripheral grinding face and an 8" inside diameter or arbor in which it is desired to insert reinforcing elements at 1,/4 intervals across the thickness of the abrasive body, the conventional process of making such wheels would involve a filling of the mold with an initial 1A thickness of abra sive-bond mixture, insertion of a reinforcement, and then putting in another 1A thickness of abrasive mixture, striking off, and the insertion of another reinforcement, and so on until the desired thickness of Wheel was obtained when compacted. Similar procedure can also be used to make reinforced resinoid snagging wheels in accordance with asaaore the present invention in which a series ofl separate reinforcements of the composite type herein described are used. However, prefer to reinforce such thick abrasive wheels and other types of abrasive wheels of substantial volume or thickness by a preferred method wherein a single reinforcement in continuous helical form is embodied within the wheel with the abrasive mixture incorporatedl between the turns ofthe helical reinforcement by loading the spaces between the turns of the reinforcement with abrasive grain and bond from the central arbor of the wheel by means of centrifugal force.

Referring to Figure 3, a reinforcement 2li in the form of a single continuous helical' structure is inserted in the mold with the outside peripheral edge of the reinforcing structure against the inside of the mold barrel and with the individual turns of the helical reinforcement held apart by suitable spaces. The abrasive grain and bond is then injected by suitable means intotthe mold byy centrifugal force to fill the spaces between the turns of the helical reinforcement, the excess abrasive grain removed, and the entire assembly compacted under pressure and cured to form a reinforced abrasive wheel of the desired thickness. Figure 3 shows diagrammatically the manner in which the combustible component of the reinforcement acts to burn away the brous material of the reinforcement at the peripheral grinding surface 21 of the wheel to provide a series of clearance spaces 2.2 extending across the face of the wheel in the form of a continuous spiral In addition to the removal of the reinforcing material from the grinding face of the wheel where it would otherwise interfere with the cutting performance of the wheel, these clearance spaces as so disposed add to the effective cutting action by providing the wheel with a multiplicity of generally peripheral cutting edges which move progressively across the face of the wheel as the wheel rotates in contact with a work piece being ground.

An alternative manner of making a reinforced resinoid bonded snagging Wheel of the type shown in Figure 3 is to apply a coating of abrasive grain and bond to the helical reinforcement, on one or both sides thereof, and then before the resin bond is fully cured, place a continuous length of the abrasive coated helical reinforcing material in a mold and compact it under pressure to form a wheel of the desired thickness. The wheel is either cured simultaneously with the pressing operation and/or subjected to a subsequent oven curing.

While i have described under Example Il an abrasive Wheel reinforced by the incorporation within the body of the wheel of a single continuous helical reinforcement it is to be understood that abrasive articles and other bodies can be similarly reinforced in accordance with the same principles but in which the reinforcements take the form of a double or multiple helix or helices. For example, it may be desirable to increase the pitch (pitch can be defined as the distance a point on the helix will advance axially of the helix in one revolution of the helix) of the reinforcing element within the body of the article. Although this can be done by increasing the coarseness of the pitch, l have found it preferable in, e. g., the reinforcing of abrasive wheels, to use a multiple or compound helix, such as a double or triple helix obtained by the interleaving of two or three or more helical reinforcements with one another. By using more than one helix the number of sharp cutting edges per unit linear length across the face of the grinding wheel can be increased, thereby promoting greater cutting efficiency and controlled breakdown or self-dressing action to the wheel, as well as giving a stronger wheel with smoother performance.

Example lli7 rIhr: present invention is not confined to the making of abrasive wheels composed solely of abrasive grain and bond according to conventional molding procedures, but can also be applied with equal effectiveness to the making of-that type of abrasive wheel composed of a plurality of layers of abrasive-included fibrous sheet material. Melton et al. U. S. Patent 2,355,667 issued August l5, 19.44, and Goepfert et al. U. S. Patent 2,540,112 issued February 6, 1951, describe fully the methods for making such abrasive-included fibrous wheels.

Following the procedural practices set forth in either of those two patents, and using the specific composite reinforcements disclosed and described herein, highly satisfactory abrasive wheels of improved performance characteristics and increased strength have been made. For example, Figure 5 shows a representative abrasive wheel of this type embodying two reinforcements 24 and 25 embedded within the wheel adjacent the side faces. As in the more conventional type of bonded abrasive body, the reinforcements likewise are disintegrated as they approach the grinding surface of the wheel so as not to interfere with the normal grinding action of the product.

Although several specific embodiments of the present invention have been set forth above, the invention is not to be confined or limited to such illustrative articles. Cup-shaped wheels and other forms of abrasive products Ican be similarly reinforced in accordance with the practices of the present invention. Itis also within the scope of the present disclosure to embody reinforcements of different character such as other forms of woven or nonwoven iibrous structural material, individual strands of reinforcement disposed throughout ythe wheel body in any desired arrangement, the sole requisite being that the reinforcing element be of composite character consisting of a high tensile strength reinforcing base material in close association with a combustible or pyrophoric material which will disintegrate and also cause the high strength element of the reinforcement to disintegrate when the reinforcing element or elements approach the grinding surface of the article.

Having described the invention in detail it is desired to claim:

l. An abrasive wheel comprising a molded body comprising abrasive particles and a bond therefor, said body containing at least one reinforcing element comprising a layer of lilamentary material bearing a readily oxidizable metal which will ignite when exposed to the heat of grinding to disintegrate said ilamentary material adjacent the grinding face of the Wheel.

2. An abrasive article of the bonded type containing a composite reinforcing element consisting essentially of a high strength iilamentary base and bearing a readily oxidizable metal ignitable at the heat of grinding whereby the said tilamentary material is disintegrated at the grinding surface of said article.

3. An abrasive wheel comprising abrasive grains and a bond, the body of said wheel having embedded therein and extending substantially from the arbor to the periphery of said wheel at least one layer of composite reinforcing material consisting essentially of a high strength lamentary material and a pyrophoric substance which will ignite at the heat of grinding and disintegrate the reinforcing material adjacent the wheel periphery.

4. An abrasive article according to claim 3 in which the lamentary material of the reinforcing element is nylon.

5. An abrasive article according to claim 3 in which the filamentary material of the reinforcing element is ne steel wire.

6. An abrasive article according to claim 3 in which the filamentary material of the reinforcing element is fiber glass yarn.

7. An abrasive wheel comprising abrasive grains and a bond, the body of said wheel having embedded therein at least one layer of tbrous reinforcing material disposed substantially normal to the abrading surface of said wheel,

said reinforcing material having thereon a coating of magnesium metal powder whereby the reinforcing layer will disintegrate at the grinding surface of said wheel in the course of grinding.

8. An abrasive wheel according to claim 7 in which the fibrous reinforcing material is of a nylon fiber base.

9. An abrasive wheel according to claim 7 in which the fibrous reinforcing material is of a glass fiber base.

10. An abrasive wheel according to claim 7 in which the brous reinforcing material is of a steel wire base.

11. An abrasive wheel comprising a plurality of layers of abrasive-included fibrous sheet material, said wheel having embedded therein at least one layer of fibrous reinforcing material disposed substantially normal to the abrading surface of said wheel, said reinforcing material having thereon a coating of magnesium metal powder whereby the reinforcing layer Will disintegrate at the grinding surface of said wheel in the course of grinding.

12. An abrasive wheel comprising a plurality of layers of abrasive-included fibrous sheet material, the body of said Wheel having embedded therein and extending substantially from the arbor to the periphery of said wheel at least one layer of composite reinforcing material consisting essentially of a high strength flamentary material and a combustible substance which will ignite at the heat 10 of grinding and disintegrate the reinforcing material adjacent the Wheel periphery.

13. An abrasive article of the bonded abrasive type, the body of the article being reinforced with at least one layer of a two component reinforcing material comprising a high strength fibrous component as support for a pyrophoric component.

14. An abrasive article of the bonded type containing a composite reinforcing element consisting essentially of a high strength filamentary base and a readily oxidizable metal ignitabie at the heat of grinding whereby the said frlamentary material is disintegrated at the grinding surface of said article, said reinforcing metal being finely divided magnesium.

References Cited in the file of this patent UNITED STATES PATENTS 2,092,591 Sohlstrom Sept. 7, 1937 2,094,556 Anderson Sept. 28, 1937 2,275,339 Allison Mar. 3, 1942 2,643,494 Erickson June 30, 1953 2,656,654 Erickson Oct. 27, 1953 FOREIGN PATENTS 51,014 Norway Feb. 23, 1931 

13. AN ABRASIVE ARTICLE OF THE BONDED ABRASIVE TYPE, THE BODY OF THE ARTICLE BEING REINFORCED WITH AT LEAST ONE LAYER OF A TWO COMPONENT REINFORCING MATERIAL COMPRISING A HIGH STRENGTH FIBROUS COMPONENT AS SUPPORT FOR A PYROPHORIC COMPONENT. 